New HIV drug types hailed as ‘remarkable’

LOS ANGELES – In what some are hailing as the most important development in HIV therapy in a decade, two new classes of drugs have been found to block virus replication in patients who have become resistant to existing drugs, researchers said Tuesday.

The two new classes, called integrase inhibitors and CCR5 inhibitors, doubled the number of patients in a group of studies whose infections could be brought under control, researchers said at the Conference on Retroviruses and Opportunistic Infections at the Los Angeles Convention Center.

This is “a pivotal moment” for patients who have become resistant to most AIDS drugs, said Dr. Eric Daar of Harbor-UCLA Medical Center. Daar, who was not involved in the research, estimated that about 20 percent of his patients are resistant to the existing classes of drugs.

Given the serious problems in treating drug-resistant patients, Daar said the finding “brings the opportunity for a new life.”

Dr. John Mellors, of the University of Pittsburgh, said the new findings hearken back to the introduction of the powerful drugs in the 1990s that converted HIV infection from a mostly fatal disease to one that could be managed for long periods of time. “This is really a remarkable development in the field,” said Mellors, who was not involved in the studies.

Closest to federal approval is maraviroc, developed by drug maker Pfizer Inc. The drug binds to a receptor on the surface of human cells, known as CCR5, preventing HIV from locking on and entering the cells.

Maraviroc represent the first class of HIV drugs that targets the human immune system rather than the virus itself.

Several other companies have attempted to bring out CCR5 inhibitors, but with little success. Trials with GlaxoSmithKline’s candidate, aplaviroc, were halted in 2005 because the drug was toxic to the liver.

Dr. Howard Mayer of Pfizer reported on studies of maraviroc in 1,049 patients in 13 countries: 840 received the experimental drug in combination with their regular drug regimen, while the rest received a placebo and their regular drugs.

About 44 percent of the patients receiving maraviroc saw their blood HIV concentrations fall to undetectable levels after 24 weeks of therapy, Meyer said, compared with 23 percent of those receiving placebo.

Experts believe the drug could be approved by the Food and Drug Administration by the end of the year.

The second new drug is Merck & Co.’s raltegravir, formerly known as MK-0158. It blocks an HIV enzyme called integrase, one of three enzymes used by the virus to copy itself in human immune cells.

Dr. David Cooper from the University of New South Wales in Australia and Dr. Roy Steigbigel from State University of New York at Stony Brook reported on two studies involving 699 patients, two-thirds of whom received raltegravir in addition to their regular HIV drugs. Both studies were funded by Merck.

About 62 percent of the patients receiving raltegravir saw the HIV in their blood fall to undetectable levels after 16 weeks, compared with 35 percent of those receiving the standard drugs alone, the researchers said.

The drug, which has been fast-tracked by the FDA, was well-tolerated by patients. Its side effects, which were similar to those of the standard drug regimen, included gastrointestinal bloating, diarrhea and nausea.